This invention relates generally to magnetic recording apparatus or method therefor, and particularly, the present invention relates to tape speed control for producing a master tape carrying digital signals, from which master tape the digital signals are copied to a plurality of slave tapes.
When it is intended to produce a plurality of copies of magnetic recording tapes by way of tape-to-tape copy technique, a master tape is first produced and then the contents or information prerecorded in the master tape is reproduced or read out to record the same onto slave tapes one after another. In the case that the information to be copied is an analog signal as in analog audio cassette tapes or open reel tapes, the information can be copied from a master tape to a slave tape at a relatively high speed. Namely, signals respectively recorded in respective tracks are simultaneously read out by means of a multi-track head, and the read out signals are simultaneously recorded on multi-tracks on the slave tape.
However, when it is intended to copy a magnetic recording tape carrying digital signals having a configuration of blocks or frames as PCM (pulse code modulated) signals, tape-to-tape copy cannot simply be effected. In the case that signals on different tracks have been recorded on a master tape in one direction of the tape as in a magnetic recording tape used for computers, the signals may be read out by a multi-track head and then recorded by another multi-track head to produce a copy. However, in the case that some tracks have been recorded in one direction and the remaining tracks have been recorded in an opposite direction in the same manner as in normal music cassette tapes, the phase relationship between one group of tracks and the other group of tracks, both recorded in opposite directions, is not necessarily uniform or constant throughout the entire length of the magnetic recording tape due to the variation in tape speed on recording.
As is well known, digital signals derived from a master tape have to be processed prior to recording the same on slave tape or tapes in order to correct possible errors due to jitter, skew, dropout or the like. When processing the digital signal read out from the master tape, a synchronous signal indicative of the position of data on the master tape is required. Such a synchronous signal may be derived from a control track, in which a predetermined synchronous or timing signal is prerecorded, or from one of data tracks in the case that the digital signal has a block or frame configuration.
However, when digital signals are recorded on a plurality of tracks of two groups in two directions as described in the above, a derived synchronous signal represents the position of data of only one of the two groups. Therefore, although a synchronous signal derived from a track of one group can be simply used for processing read out data from tracks of this group, it cannot be simply used for processing data read out from a track of the other group because of the phase difference between signals of the two groups of tracks. Namely, if it is intended to effect tape-to-tape copying by using a master tape on which bits of a digital word are recorded on multitracks in two directions, a complex timing control device would be needed for compensating for the phase difference between two groups of tracks so that read out data are correctly stored in appropriate memories from which data will be read out in synchronism with clock pulses to be recorded on a slave tape. Furthermore, such a possible technique requires a large capacity of the memories.
For these reasons, in conventional techniques digital data having a configuration of blocks or frames prerecorded on a master tape in two directions had to be reproduced in two directions separately one after another.